Xref: utzoo sci.electronics:8284 sci.crypt:2404 Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!cs.utexas.edu!uunet!n3dmc!johnl From: johnl@n3dmc.UU.NET (John Limpert) Newsgroups: sci.electronics,sci.crypt Subject: Re: Telephone privacy gadgets Add: Cryptography Message-ID: <804@n3dmc.UU.NET> Date: 20 Oct 89 06:18:38 GMT References: <799@mccall.uucp> <776@ariel.unm.edu> <790@ariel.unm.edu> <1989Oct19.154929.19256@utzoo.uucp> Reply-To: johnl@n3dmc.UUCP (John Limpert) Followup-To: sci.electronics Organization: N3DMC, Silver Spring, Maryland Lines: 21 In article <1989Oct19.154929.19256@utzoo.uucp> henry@utzoo.uucp (Henry Spencer) writes: >In article <790@ariel.unm.edu> ee5391aa@hydra.unm.edu.UUCP (Duke McMullan n5gax) writes: >>Expensive and easy to defeat -- probably... > >Most any non-digital scrambler, no matter how tricky, is probably going to >fall under this heading. There is lots and *lots* of redundancy in the >human voice, and it's very hard to hide it completely. I read a book on HF radio frequency assignments that said the Department of Energy used a scrambler system for the trucks that transport nuclear materials. The system divided the audio spectrum into a number of frequency bands and shuffled them around before feeding the audio into the transmitter. The interesting part of the system was the use of some sort of key generator to change the mapping at a rapid rate. I don't know how difficult it would be to reconstruct the original signal by attempting to match up parts of successive samples. The nice thing about this system was that it worked with conventional radio equipment. -- John A. Limpert I'm the NRA! Internet: johnl@n3dmc.UU.NET UUCP: uunet!n3dmc!johnl